1. Field of the Invention
This invention generally relates to optical systems which employ electromechanical control systems. More particularly, this invention relates to the automatic control of a pinhole aperture spatial filter from which a laser light beam is expanding in order to achieve and maintain alignment of the expanding laser beam.
2. Discussion of the Prior Art
In any optical system, such as optical correlator systems, it is necessary to achieve and maintain alignment of an incoming laser beam. The correct spatial geometry in optics systems is critical for proper system operation and optimal system performance. The incoming laser beam is easily thrown off axis by the various lenses and apparatus it must pass through; therefore, there must be some method to achieve and maintain alignment of the laser beam. The accepted practice has been to do this by hand.
One such procedure involves utilizing a small low powered laser which emits a narrow parallel beam, and making a mark with a small ink dot in the middle of each lens in the system. By having the small laser aimed along the optic axis of the system, it can be easily seen if the beam passes through the ink dots thereby indicating if the components in the system are properly aligned. Obviously this is not an exact measurement and alignment system; however, it does provide a rough tuning of the system. The above technique is particularly useful in systems that employ mirrors because the mirrors can be manuevered to focus the beam along the optical axis of the system.
The process of beam alignment when done by hand involves measurement and adjustment by a human operator. This is a trial and error process that might require that system operation be suspended. This process is laborious and time consuming, especially if great precision is required as in most optics applications. In addition, in some applications it may not be practical for a human operator to be present, such as in an unmannered space craft; therefore, other techniques such as automatic alignment systems, which comprise automatic control systems, have increasingly become of interest.
The present invention solves the problems and limitations of the previous methods of laser beam alignment by providing applications for the automatic alignment of a pinhole aperture spatial filter in an optical system, such as those used in optical correlator systems, such that the input laser beam retains its integrity during system operation. There is a need, therefore, for an automatic laser beam expander, pinhole alignment system which provides for the automatic expansion and alignment of an incoming laser beam, maintaining this alignment, and accomplishing this during system operation with a high degree of precision.